Current treatment of chronic anal fissure continues to be based on conventional conservative measures in a high percentage of cases. What is known as chemical sphincterotomy aims to achieve a temporary decrease of anal pressures that allows fissures to heal. There are various alternatives such as nitroglycerine or diltiazem ointment and botulinum toxin injections. However, because of collateral effects and recurrences in the medium term, the definitive role of these treatments remains to be elucidated. Nevertheless, chemical sphincterotomy should be the first option in patients with a high risk of incontinence. "Open" or "closed" lateral internal sphincterotomy performed in the ambulatory setting with local anesthesia can currently be considered the ideal treatment of chronic anal fissure refractory to conservative measures so long as the patient is informed about the risk of minor incontinence. This procedure provides rapid and permanent recovery in more than 95% of patients. There is evidence demonstrating that the incontinence rate is related to the extent of the lateral internal sphincterotomy and consequently the extent of this procedure should be reduced to the length of the fissure.